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It is argued, that, when studying the development of social behaviour, it is valuable to investigate simultaneously several classes of social behaviour, plus locomotor, postural and manipulatory abilities. Such an approach may reveal that seemingly diverse behaviours have common ontogenetic precursors or depend upon common underlying abilities. In olive baboons, components of feeding and mouthing-and-wrestling are shown to derive from common ontogenetic precursors. Evidence suggests that mounting, riding dorsally, mouthing-and-wrestling and bipedal standing depend upon the ability to maintain postural control under difficult conditions. Some social behaviours, like grooming and presenting, appear later in development than the postural and locomotor behaviours that are used in those social behaviours. The age at which these social behaviours first appear does not seem, therefore, to be a simple function of the age at which the underlying sensori-motor skills first appear. Some vocalizations and gestures are performed in specific contexts, others are not. The contexts which evoke some of them change with age. The rationale for identifying 'precursors' of adult social behaviours is discussed. One behaviour may be the precursor of another by virtue of its form or function, or by virtue of the fact that it is controlled by a mechanism that is the precursor of a mechanism controlling the later behaviour. An early behaviour that is a precursor of a later behaviour according to one of these criteria may not necessarily be its precursor according to another. The extent to which it is valid to split an infant's activities into different classes of social behaviour is questioned.